1) Field of the Invention
This invention relates to mechanisms for testing the pressure at which safety relief valves are actuated.
2) Related Art
It is known to provide relief valves on mechanisms which have pressurized conduits or pressurized vessels. For example, relief valves are typically provided in such pressurized mechanisms as sterilizers which use pressurized steam to clean bacteria and other debris from medical instruments. If the pressure of the fluids within the conduits or pressurized vessels of the sterilizer increases significantly, the conduits or vessel may rupture, burst or otherwise fail. Therefore, relief valves are typically provided for allowing pressurized fluids within the conduits to be discharged from the system through the relief valve so that the fluid pressure in the system drops. As the fluid pressure drops, the conduits and vessel are prevented from bursting or otherwise failing. Typical relief valves are conventional check valves having a ball held by a spring against an orifice. As the pressure in the conduit increases it presses against the ball until the force of the fluid pressure overcomes the spring force and presses the ball away from the orifice. The pressurized fluid then passes through the unobstructed orifice and is thereby discharged from the conduit. The relief valve prevents the system from being over-pressurized, and thereby helps prevent the components of the pressurized mechanism from bursting or otherwise failing during operation.
It is desirable for an operator of such a pressurized mechanism to know that the relief valve is working properly and that the relief valve will discharge pressurized fluid at a pressure beneath that which would damage the conduits or tanks. It is therefore advantageous to know at what pressure the relief valve will blow. If that pressure is less than but close to the pressure that will cause the tank or conduits to fail, then the relief valve is still in good working condition. If that pressure is significantly less than or higher than the pressure that will cause the tank or conduits to fail, then the relief valve is not in satisfactory condition and must be replaced or reconditioned.
Several methods have been devised for determining at what pressure the relief valve will be actuated. Some such methods involve taking readings of the force in the spring of the relief valve and then using this reading to calculate the pressure at which the relief valve will blow. These test mechanisms have the advantage of not requiring the removal of the relief valve from the mechanism. However, the calculations can be somewhat inaccurate, in part because they are based on presumptions, such as, that the ball will not stick to the orifice. If the ball of the relief valve is not in perfect operating condition and will stick, then the presumption is not correct, and the calculation will be inaccurate.
Other test methods involve removing the relief valve from the mechanism for bench testing. The relief valve is then mounted to a tester mechanism to determine the pressure at which the relief valve will blow. These bench test mechanisms have the advantage of allowing the operator to actuate the relief valve during the test so that inaccurate calculations and presumptions are not utilized and do not create inaccurate test results. Also, bench testing mechanisms often allow the relief valve to be tested using the fluid that is present in the pressurized conduits during operation of the mechanism, which can lend itself to relatively accurate test results. However, bench testing requires that the operator remove the safety valve from the pressurized mechanism, which can be time consuming, messy, complicated, and can result in downtime for the machine.
Yet another method of testing the pressure at which the safety valve will be actuated involves increasing the pressure inside the system until the safety valve blows. An operator will slowly increase the pressure in the system while observing a pressure gauge to insure that the pressure remain below critical levels that might cause the conduits or tanks to fail. When the safety valve is actuated the operator will note the pressure of the system on the pressure gauge. The operator is thereby accurately informed of the pressure at which the safety valve will be actuated. The test is in situ such that the results will be quite accurate. No inaccurate calculations or presumptions are utilized to determine this pressure value. The safety valve is tested using the same fluid that is in the system during normal operation of the mechanism, thereby rendering relatively accurate test results. However, this type of test requires that the mechanism itself increase the fluid pressure applied to the relief valve, which places the system itself at risk of failure due to the increased pressure. Furthermore, increasing the pressure of the entire mechanism can be a lengthy process, as can be the resetting of the mechanism to its proper operating levels after the test.
Therefore, it would be desirable to provide a mechanism for testing relief valves of pressurized systems that allows such relief valves to be tested in place without requiring removal of the relief valve from the pressurized system. It would also be desirable for such a mechanism to test the relief valve while engaging the relief valve with fluid that is actually present in the pressurized system such that the test conditions replicate actual operating conditions. This would render more accurate test results. It would be desirable for such a mechanism to eliminate the need for calculations or interpolations, and that does not depend on presumptions such as that the ball will not stick in the relief valve. It would also be desirable for such a mechanism to reduce or eliminate the risks of failure of the fluid system components during such a pressure test.